| EMS (Electromagnetic stirring) technology uses a force generated by an electromagnetic stirrer to strengthen the flow of molten steel, and improve molten steel flow, heat transfer and mass transfer conditions in the solidification process in order to improve the slab solidification structure, enlarge the equiaxial grain zone and reduce the macro-segregation. This technology is widely applied to the continuous casting process to meet the needs of higher quality products. Little research has been done on steel flow and solidification of bloom continuous casting with stirring generated only by a magnetic field (M-EMS). In order to simulate the fluid flow and solidification with M-EMS in a continuous casting of a large square bloom, a 3-D magnetic field, steel flow and solidification coupled model was developed. Using numerical methods, the steel flow and solidification behavior were investigated in the electromagnetic continuous casting process.The reasonable design and improvement of the stirring efficiency of the EMS stirrer are important problems in electromagnetic stirring. In order to determine reasonable stirrer structural parameters using the finite element method, the three-dimensional distribution of magnetic flux density and the electromagnetic force of the electromagnetic stirrer were analyzed. Then the three-dimensional steel flow in the mold for different designs of the stirring magnetic field was simulated with a finite volume method. The effects of some design parameters, such as stirrer winding form, coil current direction and other electromagnetic parameters, on the distribution of the electromagnetic force, the steel flow and solidification were investigated.Simulation results show that for an outer type electromagnetic stirrer, the maximum magnetic flux density along a central axis is located below the stirrer's height center, and gradually attenuates into the slab. The electromagnetic force is mainly concentrated on the outer layer of the slab, and attenuates as it goes into the slab. For a three-phase Clem type winding and a concentrated winding stirrer, a coil current with the same orientation can obtain a larger stirring force. As a result, the annular flow is formed in the mold, and the tangent stirring speed is larger, which is favorable for improving stirring. As the coil current increases, the stirring force acting on the molten steel increases, and the stirring intensifies. In a certain frequency range (2-10 Hz), for an external type stirrer, as the frequency increases, the electromagnetic force increases and the stirring intensifies. For a rectangular cross-section slab, the two-phase concentrated winding type stirrer has a better stirring effect than that of the three-phase Clem type winding stirrer. At times, the magnitude of the magnetic flux density does not actually correspond to the magnitude of the stirring effect. The magnitude of the stirring effect more accurately corresponds to the magnitude of the electromagnetic force or to the tangent speed of the molten steel.The impact of casting speed is a major factor in the solidification process. When the casting speed increases, the slab surface temperature increases, the solidification shell thickness becomes thin and the liquid core length extends. The uniformity of shell thickness is increased with electromagnetic stirring. At the same time it is conducive to the dissipation of overheating:the liquid core temperature and the surface temperature both decrease. As the magnitude of the stirring current increases, the position of the liquid core tends to rise upward and the thickness of the slab increases, while the change of surface temperature is minimal. As the stirring current frequency increases, the position of the liquid core tends to fall downward and the thickness of the slab decreases, but the change of surface temperature is still minimal. |
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